Calculators providing laws of the playground (5-5)

I believe the answer is:

slide-rules

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'the playground' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'calculators providing laws' is the wordplay.
'calculators providing' becomes 'slide' (I can't explain this - if you can you should give a lot more credence to this answer).
'laws' becomes 'rules' (rule is a kind of law).
'slide'+'rules'='SLIDE-RULES'

'of' acts as a link.

Can you help me to learn more?

I've seen this clue in The Daily Express.

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